instead of the nuclear bomb dropping on Rastianav, I think a pearl-harbor type event from Rykkovaa might be a better option, seeing as St Oz would respond with a Nuclear Genocide of sorts if one of their cities were nuked. Perhaps the Southern Powers would consider it but would call it "like pouring water over an ant-mound" and the main objective was just to paralyze the Ozian naval effort.
If we chose to have some Pelagian puppet ally do it, Ozia could appropriately drop a hydrogen bomb on a capital city there. When thinking about the nuclear angle, I thought of the Ozians using that event as a huge catalyst for recruitment and new-wave of religious conservatism popping up in Ozia, ending with that drop on the capital of X-tania, and the Sankta publicly condemning the event (as well as the current Primav forced out of his position) I'd rather not ruin what I had in mind though.
I'd rather not destroy Khem's Capital or anyone's capital, because it serves as a cultural symbol of someone's nation, and I don't want to limit what someone could have as a symbol because I dropped an H-Bomb on their primary nation's capital. This is why nukes get complicated and maybe an earlier era might work better, because realistically I think Ozia and many other nations would get into MAD-mode.